Our general objectives are to understand how the brain is organized for language, how dependent that organization is on language modality, and how modifiable that organization can be. We propose to study how American Sign Language, the system of hand signs developed by deaf people in the absence of speech, breaks down under conditions of brain damage. The study of sign aphasia offers a unique opportunity to insight into brain-language relations, since sign languages utilize a transmission modality different from that of spoken languages. Sign languages exhibit all the complexities of linguistic patterning found in spoken languages, but do so in a way that is unique to their modality: gramatical processes in sign language crucially involve spatial relations and the manipulation of space. We propose four major series of experiments, each bringing to bear a special property of the visual-gestural modality on investigating organization of the brain for language: 1) We explore in depth, the nature of sign language immpairments due to brain damage. We first ask whether or not sign languages are lateralized, and, if so, in which hemisphere. We then explore, if lateralization is found, wither the same neural structures subserve language function is sign and in speech. Furthermore, when language breakdown occurs in sign, we investigate the degree to which impairments are selective with respect to the various structural layers of the language. 2) We evaluate brain organization for nonlinguistic visual-spatial processing in deaf signers in order to determine whether this organization is the same as or different from the organization in hearing-speaking individuals. We further investigate the degree to which impairments in onlinguistic visual-spatial processing afect performance of a visual-spatial language. 3) We investigate the dissociability of apraxia from sign aphasia; that is, we compare the breakdown of gesture in general, with the breakdown or gestural language. 4) Finally, we explore the relation between cerebral dominance for handedness and cerebral dominance for a gestural language. This research has broad implications for the teoretical understanding of the neural mechanisms underlying the human linguistic capacity; it, should clearly contribute to our ability to remediate linguistic impairmants in brain-damaged individuals.